# Number/Related Articles

From Citizendium, the Citizens' Compendium

< Number

*See also changes related to Number, or pages that link to Number or to this page or whose text contains "Number".*

## Parent topics

- Mathematics [r]: The study of quantities, structures, their relations, and changes thereof.
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## Subtopics

- Prime number [r]: A number that can be evenly divided by exactly two positive whole numbers, namely one and itself.
^{[e]} - Whole number [r]:
*Add brief definition or description* - Rational number [r]: A number that can be expressed as a ratio of two integers.
^{[e]} - Irrational number [r]: A real number that cannot be expressed as a fraction, m / n, in which m and n are integers.
^{[e]} - Real number [r]: A limit of the Cauchy sequence of rational numbers.
^{[e]} - Complex number [r]: Numbers of the form
*a+bi*, where*a*and*b*are real numbers and*i*denotes a number satisfying .^{[e]} - P-adic number [r]:
*Add brief definition or description*

- Parts-per notation [r]: Notation used in science and engineering, to denote dimensionless proportionalities in measured quantities such as proportions at the parts-per-million (ppm), parts-per-billion (ppb), and parts-per-trillion (ppt) level.
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